Enter the Vertibird and use the machine gun to take down Synths on the roof of the building. After a while, the Vertibird will let you jump out and land on the roof. The fewer Synths you killed from the Vertibird, the more you'll have to kill on foot!

Once all are dead, head onto the second floor and locate the abandoned desk holding the Mass Fusion Executive Lab Password and Mass Fusion Executive ID.

Use the password to read the terminal in the room on the same floor level. This will locate the Beryllium Agitator. Use the Executive ID to use the elevator to get down to the lower levels.

As you ride the elevator, fight off the Synths as they appear across from you. Eventually they will cut the power and you'll be stuck at the bottom. Finish fighting them off on this level.

Locate the Mass Fusion Labs Key on a desk in a nearby room, then use the terminal (Expert) to restore power. If you get the power back on, use the elevator to travel down to the lobby.

Once there, fight off the Synths, then use the smaller elevator to get down to the lab holding the Beryllium Agitator.

Once downstairs, follow the path until you reach the decontamination room. If you try to activate the turrets or the security through the terminal before this room, two Assaultrons will appear to fight you. You can fight them now or later on in the quest.

Grab the nearby Hazmat Suit and enter the decontamination room. Once inside the radiated zone, head up the stairs and push the button. Remove the Beryllium Agitator and run out of the room!

Unfortunately, security measures have been activated. A Sentry Bot will appear. If this is your first time facing one of these beasts, the best option is to let it overheat and wait for those few seconds where it needs to cool down. The Sentry Bot will open its back and expose a Fusion Core. A few quick shots at the Fusion Core is sure to take it down! Just don't get caught in the explosion afterwards.

After the Sentry Bot, the two Assaultrons mentioned earlier will appear. Your best bet is to shoot at their torso as those will do more damage than the head.

With that clear, head back up to the lobby. Another round of Synths have appeared, but this time you have the Brotherhood of Steel to lend a hand. Once all are defeated, return to the Boston Airport and speak with Proctor Ingram to end the quest.